PHYS 212 Lecture Notes - Lecture 2: Field Line, Electric Field
● always points away from the thing exerting or creating the force
○ can be constructed using trig
● Electric field
○ electric field exerts forces; it is not the forces
○
○ same direction as the force exerted on a positive charge
○ opposite direction as the force exerted on a negative charge
○ charges in an electric field behave like masses in a gravitational field
○ Electric fields show up in
■ atoms/ions
■ muscle depolarization
■ basis for EKGs
■ electric circuits
○ Balancing using an electric field
■ Ex: what e-field could be used to suspend an electron near the earth's
surface (me = 9.11 x 10-31 kg)
● Fg is down, so Fe must be up
● electrons are negatively charged
● electric fields point in the opposite direction of the force they exert
on a negatively charged particle
● the force on the negatively charged particle must be up, so the
electric field must point down
● |Fe| = |Fg|
● Fe = q (ALWAYS TRUE)
● |qE| = mg
● |E| =
○ Field created by point charge
■ Coulomb's Law:
■ Electric field q' sees:
●
■ Electric field created by q:
●
○ Shark Boat
■ sharks can detect electric field of 5x10-5 N/C
■ if a dive board has a charge of 4 nC, how far away can the shark detect
the board
■
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Document Summary
Always points away from the thing exerting or creating the force. Electric field exerts forces; it is not the forces. Same direction as the force exerted on a positive charge. Opposite direction as the force exerted on a negative charge. Charges in an electric field behave like masses in a gravitational field. Ex: what e-field could be used to suspend an electron near the earth"s surface (me = 9. 11 x 10-31 kg) Fg is down, so fe must be up. Electric fields point in the opposite direction of the force they exert on a negatively charged particle. The force on the negatively charged particle must be up, so the electric field must point down. Sharks can detect electric field of 5x10-5 n/c. If a dive board has a charge of 4 nc, how far away can the shark detect the board. For a group of point charges: find each charge"s field; add up the contribution of each.
